Quantitative sensory examination of epidural anaesthesia and analgesia in man; dose-response effect of bupivacaine.

Abstract

Time and dose-response functions of 4 concentrations of epidural bupivacaine (0.075, 0.125, 0.25, and 0.5%; 20 ml) on somatosensory and motor functions were examined in 10 healthy volunteers. Every hour for 8 h the effect of epidural bupivacaine on perception of painful and non-painful stimuli was quantified with 12 psychophysical measures. In addition knee extension strength, reaction time and skin temperature were examined. The two lowest concentrations of bupivacaine induced hypoalgesia without impairment of motor function. Epidural bupivacaine produced differential blockade of non-painful somatosensory functions in the following order: warmth perception > cold perception > perception of electrical stimuli. Epidural bupivacaine induced more pronounced hypoalgesia for short-lasting than for prolonged stimuli. A modality-related blocking order was observed for prolonged painful stimuli: heat > mechanical > electrical. It is suggested that differential blockade of somatosensory functions is caused by differences both in conduction blockade of nerve fibres and in central integration of afferent nerve impulses.